id	summary	reporter	owner	description	type	status	component	version	severity	resolution	keywords	cc	stage	has_patch	needs_docs	needs_tests	needs_better_patch	easy	ui_ux
19095	Dubious code in multiple_database tests	Aymeric Augustin	nobody	"`QueryTestCase.test_o2o_cross_database_protection` contains code that seems invalid to me.

In that test, `UserProfile` has a nullable one-to-one relation to `User`.

An unsaved instance of `User` called `charlie` is created at line 655, and a profile is attached to this instance at line 664: `charlie.userprofile = bob_profile`.

But after saving everything, that doesn't work as expected: the profile isn't linked to the user!

This is easy to understand: this line basically performs `bob_profile.user_id = charlie.id` (and populates relation caches); but since `charlie` is unsaved, `charlie.id` is `None`, hence `bob_profile.used_id` remains `None`.

I'm attaching a patch for this test case that reloads the objects and tests that `charlie.userprofile == bob_profile` ; with this patch, the test fails, proving my point.

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In #18153, I tried to catch such programming errors by raising an exception. And that breaks that test.

I think this code needs to fixed, while preserving as much of the testing behavior as possible."	Bug	closed	Database layer (models, ORM)	dev	Normal	fixed			Unreviewed	0	0	0	0	0	0